Tswaing Meteorite Crater

Tswaing Meteorite Crater as seen from the crater's rim.

On a recent visit to the Tswaing Meteorite Crater (also known as Saltpan) my wife and I were pleasantly surprised at all it has to offer nature lovers. Located approximately 40 km north-northwest of Pretoria (4), the impact crater is anomalously well preserved and home to a wide range of prolific fauna and flora. Due to its value to science and tourism the crater and its immediate surrounds form a protected area open to the public at a small entrance fee.

Impact, Geology and Archaeology:

Roughly 220 000 years ago a moderately sized meteorite hit Southern Africa forming the Tswaing Meteorite Crater. Like many meteorites the ‘Tswaing Meteorite’ was vaporised on impact. It is believed to have been 30-50 m in diameter as it sped to the Earth’s surface at 72000-108000 km/hour (2). The energy released by the impact was roughly equal to that of 1000 nuclear bomb explosions (2). Most, if not all, non-primitive life forms within a radius of about 20 km of the impact site was obliterated (2).

The Meteorite impacted the Nebo granite of the Bushveld Igneous Complex, overturning and tilting various portions of granite. Apart from the crater and structural geology of Tswaing, rapidly deformed quartz and feldspar crystals, as well as melt-breccias formed from the granite bear witness to the colossal impact event (4).

The rim of the crater has an altitude roughly 60 m higher than the surrounding country, while the crater floor lies roughly 120 m below the highest portion of the rim (1). The crater’s basin (i.e. floor) lies below the regional watertable (3). This resulted in the formation of a semi-permanent lake inside the crater, as ground- and rain water tend to flow into the crater basin (3). Due to a higher average rate of evaporation from the lake than the average rate of rain water addition to it, the lake has been saline for many millennia.

The saline character of the lake is responsible for much of the crater’s archaeological significance. Stone Age artefacts have shown that people hunted, gathered and collected salts at Tswaing from roughly 150 000 to 30 000 years before present. In historical times, between 1912 an1956, salt and soda was mined commercially at Tswaing by SA Alkali Ltd..

Biodiversity:

Black-winged Stilt is one of the bird species one is likely to encounter at the crater lake.

In terms of nature, Tswaing arguably has most to offer birders, though various mammals and numerous trees and plants occur in it. Roughly 260 bird species have been documented within the conservancy (2). This large array of birds can be attributed to the mixture of bio zones within Tswaing. They are Acacia woodland, mixed woodland (crater rim), river and wetland (wetland occurs in the north-eastern sector of the conservancy), areas where grasses dominate and the crater lake with its shores (2). The Acacia and mixed woodland attract species such as Crimson-breasted Shrike, Red-chested Cuckoo (in summer), Burchell’s Coucal, Southern Red-billed Hornbill, Cardinal Woodpecker, Fork-tailed Drongo, Brown-hooded Kingfisher, Pearl-spotted Owlet (2) and Acacia Pied Barbet (2). At the saline crater lake one can expect to see species such as Black-winged Stilt, Cape Teal, Little Grebe, Black-smith Lapwing, Pied Avocet (2) and Three-banded Plover. The wetland in the northeast of the conservancy hosts various Warblers (Willow, Icterine, Garden, Marsh, Great Reed and River), African Rail and African Purple Swamphen, to name a few (2). After high rainfall Harlequin Quail and Dwarf Bittern may visit the wetland (2). A final birding highlight I wish to mention is the African Hawk-Eagle pair that breed within the crater every year (2). The public is strongly urged not to approach the eagle’s nest, as this might interfere with the raptors’ breeding success.

Various small mammals such as rodents, mongoose, hares, genets and Vervet Monkey (2) occur at Tswaing. Larger mammals include Chacma Baboon and introduced antelope such as Impala.

Finally, for those with a passion for botany – many trees in the Tswaing have been tagged with numbers. Lists with the corresponding tree species names can be obtained at the Tswaing Museum (2).

Personal experience:

Upon entering Tswaing the first two birds we saw were Brown-hooded kingfishers...

I’ve only visited the Tswaing Crater once, but the experience has definitely motivated me to want to go again. Upon entering Tswaing the first two birds we saw were Brown-hooded kingfishers, the third species, I believe, was a White-winged Widowbird – both of which you would rarely see in Pretoria. The most prominent birdcall, evident throughout our visit, was that of the Red-chested Cuckoo, which we spotted in flight a handful of times. Other prominent vocals were those of Burchell’s Coucals and Arrow-marked Babblers.

The environment within Tswaing, especially near the crater, seemed healthy and thriving. Walking in-and-around the crater evoked a feeling of being in a remote part of Africa. This feeling was probably due to elevated humidity, pristine woodland, and the strange geomorphology of the crater.

One thing I want to do differently if I visit Tswaing again in summer – is to take lots of mosquito repellent. As soon as we started descending into the crater, we started loosing blood!

Access, facilities and costs:

The Tswaing Crater is open to the public from 07:30-16:00 everyday (2). Entrance costs R15 per adult and R20 per car (optional) and is payable at the Tswaing Museum. One may leave one’s car at the museum and enter Tswaing on foot. The entrance to Tswaing is located roughly 200 m north of the museum along the M35. Obtaining a permit for one’s car gives one access to a limited portion of the conservancies’ road network - enabling one to drive up to near the crater’s rim. A clearly marked hiking trail exists, for which a map is given on the information brochure obtained at the museum. The full length of the trail is 7.2 km (2). Day visitors can make use of the picnic area which includes braai facilities and toilets (2). Finally, camping and chalets are available at Kgotla Camp (2). For more information phone 012 790 2302.

Conclusions:

The Tswaing Crater is a must-see for Gauteng nature lovers, especially to those that enjoy birdwatching. Being only about 40 km from Pretoria – visitors from our Capital City could easily do just a morning- or afternoon visit. Visitors from further a field would probably do best to make a day-visit of Tswaing, or to sleep over at Kgotla Camp.

Denni Raubenheimer

info@wildlifestockimage.com

References:

1) Brandt, D. and Reimold, W.U. (1995). The geology of the Pretoria Saltpan impact structure and the surrounding area. South African Journal of Geology, 98 (3), 287-304.

2) Marias, E. and Peacock, F. (2008). The Chamberlain Guide to Birding Gauteng. Mirafra Publishing, Cape Town. – 384pp.

3) McCaffrey, L.P. and Harris, C. (1996). Hydrological impact of the Pretoria Salt Pan crater, South Africa. Journal of African Earth Sciences, 23 (2), 205-212.

4) Partridge, T. C., Demenocal, P. B., Lorentz, S. A., Paiker, M. J. and Vogel, J. C. (1997). Orbital forcing of climate over South Africa: a 200,000-year rainfall record from the Pretoria Saltpan. Quarternary Science Reviews, 16, 1125-1133.